-TransForum is an innovation program which aims to make a substantial contribution to the transition towards more sustainable development of the Dutch agricultural sector. This article describes the scientific foundation and architecture of this program. TransForum operates on the basis of five working hypotheses which together constitute one integrated analytical framework. These hypotheses are: (1) sustainable development is a dynamic system property; (2) sustainable development needs system innovation; (3) system innovation is a non-linear learning process; (4) system innovation requires active participation of relevant key players from knowledge institutes, governmental bodies, civil society organisations and the business community; (5) the program requires transdisciplinary collaboration of all players. TransForum identifies three new innovation strategies: (1) vital clusters; (2) regional development; (3) international agro-food networks; as alternatives to the current arrangements. Innovative projects are organised in these innovation strategies. The aim of the scientific program is threefold: (1) it addresses research questions raised in the innovative projects; (2) it investigates the need for system-innovations and the way in which they can be realized; (3) it designs research projects to test the 5 main working hypotheses of the program. The scientific program is organised in four themes following a cyclic innovation process which is constantly monitored. The cycle starts with people's preferences and images, followed by studies on which inventions are required to achieve a successful innovation. Subsequently, it is investigated how to organize new innovations and transitions and finally, how citizen/consumers behaviour and preferences mobilizes sustainable development, closing the loop. sustainable development / transition / system innovation / networks

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The senescence of flower petals is a highly regulated developmental process which requires active gene expression and protein synthesis. The biochemical changes associated with petal senescence in carnation flowers include an increase in hydrolytic enzymes, degradation of macro-molecules, increased respiratory activity and a climacteric-like increase in ethylene production. It is clear that the gaseous phytohormone ethylene plays a critical role in the regulation and coordination of senescence processes. Many reviews on physiology and mode of action of ethylene are available. Molecular cloning led to the isolation of genes involved in ethylene biosynthesis and action. This review describes the current status of the studies on regulation of ethylene biosynthesis and ethylene response in carnation flowers. An overview is given of studies on senescence-related gene expression and possibilities to improve postharvest longevity by genetic engineering.Abbreviations: ACC = 1 aminocyclopropane-1-carboxylic acid; AIB = o-amino-isobutyric acid; AOA = amino oxyacetic acid; AVG = aminoethoxyvinyl glycine; DACP = diazocyclopentadiene; EFE = ethylene forming enzyme; MACC = malonyl 1 aminocyclopropane-1-carboxylic acid; MTA = S-methylthio-adenosine; NBD = 2,5 norbomadiene; ppb = parts per billion; SAM = S-adenosyl-methionine; STS = silver thiosulphate.

Adventitious shoot formation from leaf explants of carnation (Dianthus caryophyllus L.) was investigated. The two leaves from one node of in vitro-grown plants showed different shoot-forming potential, depending on the order in which the leaves were removed from the stem. The leaf removed second formed more shoots and also had a large amount of adhering stem tissue. Explants with equal amounts of adhering stem tissue were obtained by making two incisions through the fused leaf bases, prior to their removal, resulting in an improved shoot formation. The procedure developed for leaf explants from in vitro-grown plants was also applied to leaf explants from greenhousegrown plants. Shoot formation from leaf explants taken from greenhouse-grown plants was further improved by cutting the leaf explant longitudinally into two parts.Abbreviations: BA -benzyladenine, NAA -a-naphthaleneacetic acid Adventitious shoot formation for carnation (Dianthus caryophyllus L.) has been obtained from petals (Kakehi 1979), axillary buds (Miller et al. 1991), stems (Nugent et at. 1991 and leaves from in vitro-grown plants (van Altvorst et at. 1992). The procedure described by van Altvorst et at. (1992) allowed production of more than 10 adventitious shoots per explant with up to 65 % of the explants showing adventitious shoot formation. This procedure was also successfully applied to a wide range of cultivars belonging to all major carnation types. Since shoot formation was restricted to the base of the leaf, the best way to isolate the leaves was to carefully tear them from the stem using forceps while keeping the leaf base intact. The leaf that was removed second gave a much higher shoot regeneration response, possibly because of the larger amount of basal leaf tissue that remained attached to the leaf explant. In this paper, we further analyze the relation between shoot regeneration response and the adhering stem tissue. The shoot regeneration responses of leaf explants from in vitro-and greenhouse-grown plants were compared. The efficiency of adventitious shoot formation was further improved by modifying the preparation of the explants.The carnation plants (Diantini type, CPRO clone 89086) were obtained as rooted cuttings from a commercial source and were grown in a greenhouse at 16/14 °C (day/night). Nodal cuttings from greenhousegrown plants were surface-disinfested and cultured in vitro as described by van Altvorst et al. (1992). Explants from greenhouse-grown cuttings and from in vitro-grown plants were taken from the three leaf pairs just below the apex. The two leaves of one pair were carefully removed from the stem using forceps in such a way that the axillary bud remained attached to the stem (Fig. la). The order in which the leaves of each pair (first and second) were removed from the stem was recorded and the explants were cultured on shoot regeneration medium. This shoot regeneration medium contained MS salts and vitamins (Murashige & Skoog 1962) supplemented with 3% (w/v) sucrose (MS-30), 4 ~tM BA, 1.6 ~tM NAA and 7 g 1-...